The ability to treat discriminatively different external stimuli as members of a common class is the defining attribute of conceptualization. Prior work has shown that animals as diverse as human beings and pigeons can classify lifelike visual stimuli into natural and artificial categories. The present proposal aims to determine whether the perceptual processes of conceptualization are similar in humans and pigeons. Pigeons will be trained with operant conditioning procedures to discriminate line drawings of natural and artificial stimuli. They will then be tested with specially-modified stimuli that delete certain portions of the training stimulus, that rearrange its component parts, or that rotate the image in the plane or in depth. These test stimuli produce highly selective effects in humans, which have encouraged the view that we categorize objects by means of a piecemeal perceptual process-recognition by components. If people and pigeons similarly process visual stimuli, then the results of the planned series of experiments with pigeons should parallel those obtained earlier with people. Empirical convergence would surely attest to the economy of nature and to the superfluity of language for conceptualization. Empirical divergence would imply that different neurobiological or linguistic mechanisms mediate visual concepts in people and pigeons.